DE3941706C1 - - Google Patents

Description

The invention relates to a device for isotropic delivery and for the isotropic absorption of light according to the generic term of Claim 1.

In generic devices, a weakly absorbent Diffuser attached to the flat, distal end of an optical fiber.

With isotropic emitters, the LWL (= fiber optic cable) a divergent light beam symmetrical to its axis from. (Theoretical maximum value of the divergence or acceptance common quartz glass fibers: approx. 30 °).

Photons that have penetrated into the scattering body change direction depending on the distance covered and the Scattering particle density several times. This leads to ideally only an omnidirectional radiation.

With isotropic detectors, photons penetrate from any spatial direction into a spherical scattering body in which it lose their original direction. Photons inside of the acceptance angle meet the flat end of the light guide, can enter the fiber optic.

These principles lie with all known developments isotropic emitters or detectors. So far, only the design of the diffuser has been varied or its attachment to the fiber optic cable, but not the end surface geometry of the fiber optic in the sense of a targeted influence its radiation or detection characteristics.

U.S. Patent No. 4,693,556 to Mc Caughan, Jr. refers to a process for the production of scattering bodies which is subject to UV serving hardening suspension of glue and scattering particles. This is applied in layers on a flat fiber optic end  and hardened, whereby after several operations the Diffuser is created.

In Advances in Laser Medicine, Safety and Laser tissue interaction (Editors: G. J. Müller, H. P .: Berlien), ecomed, Landsberg, 1989, pages 358-368 described W. M. Star and J. P. A. Marÿnis the manufacture of isotropic detectors made of drilled plastic balls glued onto the fiber optic end.

In Photodynamic Therapy of Tumors and Other Diseasas (editors: G. Jori, C. Perria), Liberia progetto editore padova, 1985, pages 371-385 describes V. Russo u. a. conical distal FO ends. However, this is only a side view (Ring-shaped) light emission. A mathematical connection between the cone angle and the radiation pattern not manufactured (the etching technique used to manufacture it of cone ends is anyway difficult to reproduce).

From DE-OS 21 31 500 it is known a fiber optic cone to train. The FO is a gradient light guide and conical formation is said to be optimal coupling of cause parallel radiation in the light guide.

An isotropic radiation characteristic cannot be used to reach.

Furthermore, an irradiation device is known from US Pat. No. 4,740,047 known in which a beveled on one side LWL is surrounded by a covering that between the LWL End and the envelope creates a cavity.

This makes the radiation pattern extremely asymmetrical.

In all known solutions, the axially directed radiation characteristic of the fiber optic only incompletely into a spherical symmetry Characteristic converted. A too ineffective radiation in the rear hemisphere. This is due to:

Shading by connecting elements between the diffuser and LWL as well as by the LWL itself (connecting elements e.g. B. necessary if the power density on the light entry surface of the scattering body by increasing the distance between fiber and diffuser must be reduced).

Limited optimization of the light deflection if the Diffuser dimensions (endoscopic applications!) And Absorption losses (overheating of the scatter body!) Small to be held.  

Common isotropic emitters (diameter: 3-4 mm) are closed great for most endoscope and catheter channels. A reduction the radiator dimensions should therefore be aimed for. At the same time output powers of at least 2 W are required. When using flat light guide ends, both goals can be achieved cannot be achieved because of an unacceptable deterioration the radiation pattern would be the consequence.

The known isotropic detectors are characterized by small Sensitivity.

The light guide with a flat fiber end has one in comparison small entry surface to the surface of the diffuser at which Photons only in a very narrow solid angle range (maximum acceptance approx. 30 °) can occur.

To ensure sufficient light deflection in the diffuser, the scattering particle density must be chosen so high that a large proportion of the incident light from the Scattering body is scattered back.

The invention has for its object a device for the radiation and light detection in hard to reach Cavities over fiber, e.g. B. in medical laser applications like the integral photodynamic therapy of hollow organs to develop. It should be as spherical as possible Directional characteristics can be realized with small diameters.

This object is achieved by the characterizing Features of claim 1 solved. Describe the subclaims advantageous embodiments of the invention.

The device according to the invention can in particular achieve the following advantages.  

The scatter body is functionally relieved, i. H. he just has to the radiation or detection characteristic of the light guide end smooth.

The total number for a spherically symmetrical radiation or detection required scattering decreases. From the possible reduction of the scattering particles (density) follows:

A lower absorption loss in the scattering body and thus a high threshold for a heater defect due to overheating.

Reduction of detection losses through backscattering at the Diffuser surface.

In comparison to the flat fiber end, the cone end irradiates always a significantly larger area, e.g. B. in a cylindrical Bore of the scatter body. A reduction in the power density due to the fiber optic attachment at the back can therefore be avoided. Shading to the rear is thus on the optical fiber itself reduced and thus minimized.

Compared to conventional designs are smaller Spotlight dimensions and a more homogeneous radiation pattern possible with at least the same load capacity.

The conical fiber optic end detects over a large area allowed entry angle and thus has a higher Sensitivity as a flat fiber optic end.

If desired, you can do this by specifically varying the cone angle also stressed radiation from the rear hemisphere respectively.

This is advantageous if the radiator is integrated in a catheter increases shadowing through the catheter are to be feared.  

With integral photodynamic therapy after tumor selective Enrichment of a photosensitizer in the organ wall tumors and neighboring healthy tissue become a common, ideally locally constant over the entire organ wall Light dose applied.

The homogeneous illumination required for this is achieved in spherical illumination Organs like the bladder best with the help of a "isotropic" radiator approximately spherical symmetrical radiation.

Based on clinical experience, a suitable one isotropic emitter especially following requirements deliver:

The radiation pattern should be as sectoral as possible be balanced, asymmetries especially to the disadvantage of the rear hemisphere to be avoided.

Its continuous power output must be at least 2 watts amount to the required light energy in an acceptable To be able to apply treatment time.

The radiator must be in clinical endoscope or catheter systems can be integrated (diameter of self-supporting diffuser: significantly smaller than 3 mm).

For simulations in laboratory setups, lower output rates, optimized radiation characteristics and depending on the intended use minimized dimensions required.

Two embodiments of the invention are as follows explained in more detail with reference to the figures.

Here, FIGS. 1 and 2 Examples of the spotlight, and

Fig. 3 shows a central longitudinal section through the distal end of the optical waveguide.

Figs. 1 and 2 show an optical fiber with a core 1, cladding 2 and the jacket 3, the distal end surface 4 has one of the following forms: cone, truncated cone with each cone angle. 5 A medium 6 that surrounds the fiber optic end and is optically thinner than this. A diffuser 7 , which is attached to the fiber optic jacket 3 by means of the connection 8 .

The scattering body is a self-supporting body made of a carrier material (e.g. plastic, glass or composite) and a scattering substance (e.g. BaSO₄, TiO₂) whose diameter is less than 5 mm and in which the ratio of Diffuser body to fiber optic jacket diameter is greater than 2.

Variant I ( Fig. 1) shows a solid, preferably spherical, diffuser with a blind hole for receiving the optical fiber and

Variant II ( Fig. 2) a preferably hollow spherical diffuser with a tubular guide for receiving and attaching the fiber.

The diffuser 7 has the following optical properties:

Variant I:
Absorption in 7 : <10%
Backscatter from 7 in 6 : <50%
Transmission through 7 : <50%

Variant II:
Absorption in 7 : <10%
Backscatter from 7 in 6 : <50%
Transmission through 7 : <50%

The required refractive index of the medium-filled space 6 depends on the refractive index of 1. The index ratio 3 to 6 must be greater than 1.3.

The conical end 4 of the optical fiber 1, 2, 3 is used for controllable light emission in the front (beam angle to the optical fiber axis: β _a <90 °) and in the rear hemisphere β _a <90 °). The light distribution on both hemispheres is dependent on the cone angle 5 , on the angular distribution of the photons before the first interface contact (represented by the angle between the photon paths and the fiber optic axis) and the ratio of the refractive indices n₁ and n₆ of 1 and 6 as follows achieve:

Assuming that the fiber optic core 1 is optically denser than the surrounding medium 6 , two phenomena are possible when a photon in the fiber optic contacts the interface:

• 1st refraction: the photon emerges from the optical fiber, it changes its shape Direction according to the refraction law.
• 2. Total reflection: the photon remains in the optical fiber, it changes its direction according to the law of reflection.
  The critical angle of total reflection α _g and the impact angle α 10 of the photon to the interface normal determine which phenomenon occurs. The following applies: refraction: | α | α _g (1) total reflection: | α | <α _g (2) In conical fiber optic ends the following applies to the impact angle α at the nth interface contact (two-dimensional model): α = 90 ° - Φ - δ / 2 _* (2 _* n - 1) (3) with:
  Φ: angle between photon path and fiber optic axis before the first interface contact (positive sign: photon path points away from the fiber optic axis and vice versa, in Fig. 3: 9)
  δ: cone angle 5 (angle between the surface lines)
  The following applies to the radiation angle 11 β _a : β _a = 90 ° - δ / 2 - arc sin (n₁ / n₆ _* sin α) The exemplary beam paths 12, 13 and 14 shown in two dimensions in FIG. 3 are of particular importance for the invention.
  The following applies to these under conditions a) and b):
  • a) Cone angle range: 80 ° δ 90 °
  • b) ratio of the refractive indices: n₁ / n₆ <1.3

12 = primary refraction (n = 1):

α α _g 0 β _a δ

Always leads to radiation in the front hemisphere.
13 = primary total reflection (n = 1), secondary refraction (n = 2):

n = 1: α <α _g

n = 2: | α | α _g approx. 70 ° <β _a <135 °.

Depending on the parameter selection, only this back hemisphere or both hemispheres are irradiated.

14 = primary total reflection (n = 1), secondary total reflection (n = 2):

n = 1: α <g _α

n = 2: | α | <α _g , α negative

This portion is reflected back into the light guide lost with it.

By varying the angle 5 (δ), the angle distribution in the optical fiber (that is, the supply of angles 9 ) and the refractive index jump 1, 6, the total photon flux through the light guide can be specifically distributed over the beam paths 12, 13 and 14 .

The conical fiber optic end enables a targeted, the properties of the scattering body appropriate light irradiation in both hemispheres.

With the conditions a) and b) (see above), the desired Backward-forward ratio v covered by 1 <v <3:

The conical fiber optic end 4 can be blunted to increase the light radiated into the front hemisphere.

For isotropic detectors, the scattering bodies 7 are constructed in exactly the same way as for the isotropic light sources.

The following applies to the conical fiber ends:

At the end of the light guide, photons can travel over a wide range of angles enter the light guide and are thus detected.

The beam paths 12 and 13 defined for the isotropic emitter are reversible, beam path 14 does not occur (geometry analogous to FIG. 3).

Detection angle β _e (analogous to 11 ) under conditions a) and b) (see radiator):

• 1: 0 ° <β _e <δ at NA (numerical aperture of the FO) = 0.4
• 2: approx. 70 ° <β _e <approx. 135 ° at NA = 0.4

The detection rates of the beam paths 12 and 13 for photons hitting the surface of the cone depend on the directional distribution of the photons - thus indirectly on the optical properties of the scattering body - on the numerical aperture of the light guide, on the cone angle 5 (δ) and on the refractive index jump 1 , 6 dependent.

The detection characteristic can be selected by a suitable choice of the above parameters optimize.  

The inventive idea is the combination of a conical one Fiber optic end with a diffuser, the radiation or detection characteristic by the cone angle in a defined area is significantly determined.

Claims (4)

1. Device for isotropic delivery and for the isotropic absorption of light, which consists of an optical waveguide, the distal end of which is located in a diffuser, characterized in that the distal end of the optical waveguide ( 1, 2, 3 ) is conical and of one at its points of contact ( 8 ) with the jacket ( 3 ) of the optical waveguide, the diffuser ( 7 ), which is firmly connected to the latter, is enclosed such that a cavity ( 6 ) is formed between the optical waveguide end ( 4 ) and the diffuser. 2. Device according to claim 1, characterized in that the stray body ( 7 ) is a hollow sphere. 3. Device according to claim 1, characterized in that the scattering body is a ball with a blind hole for receiving the optical waveguide ( 1, 2, 3 ). 4. Apparatus according to claim 1 or one of the following, characterized in that the optical fiber end ( 4 ) is a truncated cone.